With the expansion of cellular and other wireless communication services, there is a growing requirement for antennas suitable for communication with cellular telephones and other mobile user equipment. These antennas are typically provided in fixed installations on buildings or other structures in urban and other areas. The characteristic of the use of a large number of contiguous cell coverage areas of relatively small size, particularly in urban installations, results in the need for installation of large numbers of antennas. The need to provide reliable communications service to a population of users moving through coverage areas with varying transmission characteristics places special requirements on the antennas.
While many types of antennas are available for these applications, prior antennas typically have one or more of the following undesirable characteristics: limited performance, high cost, high component count and assembly labor, limited reliability, signal path and grounding connections subject to generating spurious intermodulation effects, and high susceptibility to lightning damage.
Some antenna characteristics are particularly significant in cellular and similar applications. Contacts or physical connections in the signal path and in grounding connections can, over time, degrade and result in spurious intermodulation effects which are unacceptable in many cellular applications. While configurations such as an all brass antenna construction with soldered connections can avoid contacts with resistive or bi-metallic characteristics giving rise to intermodulation effects, such construction may be prohibitively expensive. Cellular applications typically involve broad band operation susceptible to degradation where intermodulation products of the multiple simultaneous transmit signal frequencies interfere with signal reception of the received signal frequencies, for example. Thus, in cellular applications, in particular, there is a growing awareness of intermodulation product (IMP) problems, especially where contact or grounding to an aluminum ground plane is required.
Achieving high performance and reliability with low cost places emphasis on a low component count and ease of production and assembly. Adaptability to a variety of installations and operating requirements is enhanced by a construction with flexible design aspects. Adaptability to beam forming and active antenna beam steering and null control techniques is facilitated by antennas providing multiple beam capabilities. Particularly in urban locations, antenna esthetics and the capability of enabling unobtrusive antenna placement on the sides of buildings are significant objectives. Susceptibility to lightning damage can place systems out of service and result in high costs of antenna replacement.
Objects of this invention are, therefore, to provide new and improved types of dipole array antennas, and antennas having qualities which favorably address one or more of the above-identified characteristics.
Other objects are to provide antennas utilizing one or more of the following configurations in accordance with the invention:
(A) a double tuned radiating/receiving unit formed of the combination of a non-radiating exciter resonator (of rectangular or other shape and typically positioned perpendicular to a ground plane) and a dipole radiator in spaced non-contact relation to an edge of the exciter resonator (the dipole radiator of rectangular or other shape and typically positioned above the exciter resonator and parallel to the ground plane); PA1 (B) a non-contact RF ground arrangement for an input/output coaxial cable, including a quarter-wave section of microstrip line connected to the outer conductor of the coaxial cable; and PA1 (C) an RF-isolated DC grounding circuit providing lightning protection by a DC connection to ground, with a parallel non-contact low impedance RF path to ground (which is at the same time isolated from the signal distribution path by an electrical open circuit arrangement).
As will be further described, each of the above configurations (A), (B) and (C) is effective to avoid inclusion of one or more circuit connections subject to intermodulation product problems, while also avoiding high-cost, unreliable construction.